Refrigeration plants on board merchant vessels play a vital part in preservation of refrigerated cargo and provisions for the ship’s crew. In reefer ships, the temperature of the perishable goods or temperature sensitive cargo such as edible items, chemicals, or liquefied gases is controlled by the refrigeration plant of the ship.
The same plant or a smaller unit can also be used for maintaining the temperature of various provision rooms carrying food items for crew members.
STARTING
- Check oil level in the compressor’s sight glass
- Check all gauges on compressor and condenser are working properly
- Open air purge plug in front and rear covers of condenser water side to prevent water hammering
- Ensure that the condenser cooling water valves-inlet and outlet, are fully open
- Open the suction valve of the compressor till half way and fully open the discharge valve
- The crankcase heater on the compressor to be started at least 6 hours before the operation
- Fully open the refrigeration inlet and outlet valves for condenser
- Fully open the liquid outlet valve
- Fully open the stop valve before and after the back pressure regulating valve provided in the vegetable room
- Fully open the stop valve for the suction side of other rooms
- Start the cooling water pump for condenser and purge the air from it
- Check if the settings of HP and LP cut-outs are proper and then start the compressor
- Gradually open the suction valve fully while checking the suction pressure, taking care that liquid doesn't flow into the compressor
- Switch on the ozone generator in the rooms where fitted
- If any knocking noise is heard from the crankcase or excessive foaming of oil is detected, immediately throttle the suction valve
- Increase the capacity gradually before allowing the next level, so that the compressor is adjusted to new conditions
- Check the oil return pipe from the oil separator is warm
“Check the temperature of oil return piping between oil separator and compressor. If it is slightly hot than the ambient temperature, plant is in normal operation.”
STOPPING
- Stop the liquid outlet valve for the condenser
- The refrigerant will get collected in the condenser and the compressor will trip on low pressure switch
- Push the stop button of the compressor and shut the outlet and inlet valve to the compressor
- Stop the cooling water pump to the condenser and shut the inlet and outlet valves for water
- Fully close the inlet and outlet valves to the drier
- Trip the breaker for the compressor
“In case the temperature is below 0 °C while stopping the condenser, it is necessary to drain the condenser off water to prevent damage to the tubes and the cover.”
Defrosting procedure
The evaporator coils in the meat, fish and vegetable rooms are fitted with defrosting system i.e. electrical heating coil that operates at regular interval and whose timing is set by relay switch. Ensure the following:
- All the solenoid valves in the system are closed
- Compressor is stopped
- Stop the fans of meat and fish rooms
References
The Ultimate Guide to Operating Procedures of Engine Room Machinery. Anish Wankhede [2014]
